1. Field of the Invention
This invention relates to building materials, and more particularly, to a building material substrate having an improved exterior finish and method for making the same.
2. Description of the Related Art
Fiber cement in recent years has become popular for use as a building material. In many instances, fiber cement is preferred over the more conventional materials such as wood, metal, or plastics. When compared with wood, fiber cement has better water resistance and is also less prone to rotting, cracking or splitting. Moreover, fiber cement does not rust like metal and is more durable to weathering than plastics. In particular, fiber cement products such as James Hardie Building Products' HARDIPLANK® offer a lifetime of low maintenance and can be installed just as easily as wood sidings.
Advantageously, fiber cement can withstand extended exposure to humidity, rain, snow, salt air, and termites. It is also dimensionally stable and will not crack, rot, or delaminate under normal environmental conditions. Moreover, fiber cement panels may be pretextured or embossed to give the panel a desired look and feel. The panels may, for instance, be textured to resemble the look and warmth of natural wood. As such, fiber cement siding is a durable, attractive alternative to traditional wood composite, cedar, vinyl, brick or stucco sidings. Additionally, fiber cement is also an inexpensive alternative to conventional roofing materials such as corrugated aluminum sheets, which can be costly and energy intensive.
In some cases, the exterior surface of fiber cement panels is painted or subject to other types of post-production or on-site finishing to give the material the desired exterior appearance and feel for a particular application. Disadvantageously, however, natural weathering and other environmental factors can lead to chalking of the exposed paint surface and loss of polymer in the paint film. Moreover, the paint layers are typically very thin, generally on the order of one to two mils, and therefore are particularly susceptible to chipping, peeling, and scratching from surface abuse. Furthermore, the exterior surface of some building materials such as fiber cement can absorb up to about 30% water by weight, which may cause the panel to experience freeze-thaw during the winter and become damaged.
To improve the durability of the exterior surface of building materials, manufacturers sometimes bond protective films to the exposed surface so that it can better withstand exposure to the elements. The films can also be used to increase the aesthetics of the building material. One commonly used protective film is a polyvinyl fluoride (PVF) film manufactured by DuPont under the trademark TEDLAR®, which has proven to be very durable for exterior applications. However, it is particularly difficult to bond TEDLAR® or other fluorohydrocarbon films to fiber cement substrates. The adhesives used to bond TEDLAR® films to building material substrates are generally undesirable, particularly for bonding the film to the fiber cement substrate.
Conventional adhesives typically do not provide durable adhesion between TEDLAR® and fiber cement because fluorohydrocarbon films such as TEDLAR® are generally not easy to wet and to form bonds with another surface. Moreover, fiber cement has weak surface layers that can be easily peeled off if the selected adhesive cannot strongly adhere to the fiber cement. Furthermore, these adhesives generally take an undesirably long time to set, thereby causing a reduction in production throughput. Additionally, the adhesives also contain volatile organic chemicals (VOCs) that have shown to cause adverse effects on the environment. As such, the exterior finish of fiber cement substrates are often left unprotected from the elements and can become damaged by environmental conditions.
Hence, from the foregoing, it will be appreciated that there is a need for a building material assembly having a durable exterior finish that is resistant to weathering. To this end, there is a particular need for a fiber cement assembly having a protective film bonded to the exterior surface of the fiber cement substrate so as to provide the assembly with a durable finish while maintaining a desired textured appearance. Furthermore, it will be appreciated that there is a need for an adhesive system that is adapted to form a durable bond between a fluorohydrocarbon film and a substrate surface, such as fiber cement.